100-400mm MK2 focusing issue

[beastbeef]

So this is a new 100-400 MK2 on an 80D.

My settings are:

1 point manual focus, evaluating metering, back button focus, single shooting, and AI servo.

The issue is it (with full AF setting on the lens) would focus at 400mm on a far object fine, however, when I try to focus on something close >1m (above the MFD) at 400mm right after, it will not focus the AF motor will not even move, I have to manual focus a little before it would find focus.

This happens from short to long too. Does anyone have any ideas?

[RobertTheFat]

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@beastbeef wrote:

Yea everything works fine now after I changed some AF settings. Weird...

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Think of it as an expression of the fact that the lens doesn't focus as fast as the camera thinks it should.

[ebiggs1]

BTW, 

"My settings are:

1 point manual focus, evaluating metering, back button focus, single shooting, and AI servo..."

Just for kicks, reset your camera back to factory settings. Menus, tools, clear all settings and clear all custom settings. Set P mode, ISO 200, average WB.  Set and use just the center focus point. Set the lens to AF and full focus.  Now try it in good light on several subjects. (Outside on a sunny day.)   If it works, it works and all is as it should be.